Oocytes and Ovarian Follicles As Targets Of Endocrine Disrupters: Consequences For Reproductive Health

Abstract

SummaryThis chapter illustrates the physiological characteristics of oocytes and ovarian follicles in relation with their possible exposure to environmental contaminants. The total amount of oocytes present in the adult ovary is established shortly before birth. As soon as the primordial follicle store is established, follicle recruitment begins and it continues without halting for the rest of life or until the ovary is depleted. Between recruitment and ovulation, the oocyte goes through a deep transformation in order to become able to sustain embryonic development. The permanent nature of the oocyte population together with its essential role in supporting embryonic development makes it a sensitive target for the adverse effects of environmental contaminants. Amongst the different environmental contaminants we focussed our analysis on a range of chemicals known as endocrine disrupters (EDs) because of their widespread diffusion and the potential hazard they represent for reproductive health. Their sites of action include the hypothalamus-hypophyseal system, resulting in disruption of the normal pattern of gonadotropin secretion, and the ovary, resulting in destruction of the oocyte. In turn, oocyte destruction can result from directly impairing oocyte viability or from indirect mechanisms involving alterations within the follicular wall. Recent work performed in our laboratory on bovine and pig, has begun to elucidate some of the cellular and molecular mechanisms involved in EDs negative effects on oocyte developmental competence. Our results indicate that EDs perturb maternal mRNA stability and disrupt the physiological remodelling of the cytoplasm, taking place during oocyte maturation.